Consecutive Oxidation of Three H₂ Molecules by a Gold-Vanadium Oxide Cluster Cation AuVO₄ ⁺

Time-of-flight mass spectrometry experiments demonstrated that laser ablation generated and mass selected gold-vanadium heteronuclear oxide cluster AuVO₄ ⁺ can oxidize three H₂ molecules consecutively in an ion trap reactor. Quantum chemistry calculations were employed to reveal the elementary steps involved in the consecutive H₂ oxidation. The positively charged gold in AuVO₄ ⁺ functions as the active site to capture H₂ and split the H–H bond in collaboration with the terminal lattice oxygen O²⁻, during the process of which the superoxide species O₂ ^•− in AuVO₄ ⁺ is activated and then dissociated to supply enough oxygen sites for the subsequent H₂ oxidation. After the oxidation of three H₂ molecules, the Au–O bond in AuVO₄ ⁺ is converted to Au–V bond in product AuVO⁺ that is inert towards H₂. In contast, cluster AuNbO₄ ⁺ that is structurally related to AuVO₄ ⁺ can oxdize only one H₂ molecule. The origin of the different reactivities between two clusters was explored and the importance of different central metal in H₂ oxidation was emphasized.